Which of the following would be unlikely to contribute to the substrate specificity
of an enzyme?
- ANS -The enzyme has an allosteric regulatory site.
*The allosteric site is distinct from the active site, and does not affect the
substrate specificity of the enzyme.
Which of the following is NOT a way in which an enzyme can speed up the
reaction that it catalyzes?
- ANS -The active site can provide heat from the environment that raises the
energy content of the substrate.
*An enzyme cannot extract heat from the environment to speed a reaction. It can
only lower the activation energy barrier so that more substrates have the energy
to react.
The binding of a compound to an enzyme is observed to slow down or stop the
rate of the reaction catalyzed by the enzyme. Increasing the substrate
concentration reduces the inhibitory effects of this compound. Which of the
following could account for this observation?
- ANS -The compound is a competitive inhibitor.
*A competitive inhibitor slows down the enzyme by competing with the substrate
for binding at the active site. Increasing substrate concentrations will reduce the
effectiveness of a competitive inhibitor.
Which of the following statements is true about enzyme-catalyzed reactions?
- ANS -The reaction is faster than the same reaction in the absence of the
enzyme.
Reactants capable of interacting to form products in a chemical reaction must first
overcome a thermodynamic barrier known as the reaction's
- ANS -activation energy.
,A solution of starch at room temperature does not readily decompose to form a
solution of simple sugars because - ANS -the activation energy barrier for this
reaction cannot easily be surmounted at room temperature.
The active site of an enzyme is the region that - ANS -is involved in the catalytic
reaction of the enzyme.
According to the induced fit hypothesis of enzyme catalysis, which of the
following is correct? - ANS -The binding of the substrate changes the shape of the
enzyme's active site.
Mutations that result in single amino acid substitutions in an enzyme in a location
outside the active site of the enzyme - ANS -may change the enzyme's optimal
temperature or optimal pH.
In order to attach a particular amino acid to the tRNA molecule that will transport
it, an enzyme, an aminoacyl-tRNA synthetase, is required, along with ATP. Initially,
the enzyme has an active site for ATP and another for the amino acid, but it is not
able to attach the tRNA. What must occur in order for the final attachment to
occur? - ANS -The binding of the first two molecules must cause a 3-D change that
opens another active site on the enzyme.
Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV
reverse transcriptase enzyme. Unfortunately, the high mutation rate of HIV
means that the virus rapidly acquires mutations with amino acid changes that
make them resistant to these competitive inhibitors. Where in the reverse
transcriptase enzyme would such amino acid changes most likely occur in drug-
resistant viruses? - ANS -in or near the active site
Activity of various enzymes at various temperatures (a) and at various pH (b).
Which curve(s) on the graphs may represent the temperature and pH profiles of
an enzyme taken from a bacterium that lives in a mildly alkaline hot springs at
temperatures of 70°C or higher?
http://session.masteringbiology.com/problemAsset/1361593/2/0802.jpg
- ANS -curves 3 and 5
Activity of various enzymes at various temperatures (a) and at various pH (b).
, Which temperature and pH profile curves on the graphs were most likely
generated from analysis of an enzyme from a human stomach where conditions
are strongly acid?
http://session.masteringbiology.com/problemAsset/1361594/2/0802.jpg
- ANS -curves 1 and 4
Which of the following terms best describes the forward reaction in the figure?
The following question is based on the reaction A + B ↔ C + D shown in the
figure.
http://session.masteringbiology.com/problemAsset/1361595/2/0801.jpg
- ANS -exergonic, Δ G < 0
Which of the following represents the ΔG of the reaction in the figure?
The following question is based on the reaction A + B ↔ C + D shown in the
figure.
http://session.masteringbiology.com/problemAsset/1361596/2/0801.jpg
- ANS -d
Which of the following represents the activation energy needed for the
noncatalyzed reverse reaction, C + D → A + B, in the figure?
The following question is based on the reaction A + B ↔ C + D shown in the
figure.
http://session.masteringbiology.com/problemAsset/1361601/2/0801.jpg
- ANS -e
Which of the following statements about feedback regulation of a metabolic
pathway is correct? - ANS -The final product of a metabolic pathway is usually the
compound that regulates the pathway.
Protein kinases are enzymes that catalyze phosphorylation of target proteins at
specific sites, whereas protein phosphatases catalyze removal of phosphate(s)
from phosphorylated proteins. Phosphorylation and dephosphorylation can
function as an on-off switch for a protein's activity, most likely through
- ANS -the change in a protein's charge leading to a conformational change.
How does an enzyme increase the rate of the chemical reaction it catalyzes?
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